1. Field of the Invention
The present invention relates to an image forming apparatus such as a copying machine or a printer, and particularly to improvements in an image forming apparatus and treatment useful in a form of outputting an image forming job in which various images are mixed at high speed.
2. Description of the Related Art
In recent years, in an image forming apparatus using an electrophotographic treatment, more speedup of a print output has advanced while image quality is becoming higher. Particularly in an on-demand print system, each component (particularly, a developing device) of the image forming apparatus is forced to be in an image forming state always in order to output an image forming job in which various images such as a full color image or a monochrome image (for example, a monochrome K image: a monochrome black image) are mixed at high speed.
Under such circumstances, when a developing device continues to run successively with respect to an image having a low image density above all, switching of a developing agent (toner) inside the developing device is performed slightly and degradation in the developing agent is advanced and also agglomerated substances of the mutual toner are generated. When the toner agglomerated substances are accumulated inside the developing device and are delivered on an image at the time of outputting a subsequent image of a high image density, there is fear that a region corresponding to the toner agglomerates results in a white spot defect.
Means for solving such trouble includes means described in, for example, JP-A-2000-206744.
The related art described in JP-A-2000-206744 is an art in which when jobs of images with low density continue, an image of a toner discharge patch is formed in an inter-image region and toner inside a developing device is discharged by developing this toner discharge patch by toner and thus an image quality defect such as high background or variations in image density is prevented.
However, this related art treatment is a treatment in which the amount of consumption of toner is accurately detected at a previous stage of development by the developing device and when the amount of consumption of toner is small, the amount of consumption of toner is ensured using the inter-image region, and occurrence of an image quality defect such as high background or variations in image density is merely prevented by performing toner consumption processing integrally with image forming processing.
Therefore, when an image quality defect such as a white spot defect occurs with respect to quality of an image outputted actually, measures of preventing this defect at once cannot be taken and also in the toner consumption treatment using the inter-image region, an image forming area is small originally, so that it is difficult to sufficiently ensure the amount of consumption of toner and a toner agglomerated substance inside a developing agent tends to be discharged insufficiently. Particularly in the case of considering a limit of cleaning by a cleaner, an image density of discharge by the toner discharge patch cannot be increased unnecessarily and it becomes more difficult to ensure the amount of consumption of toner.